The leakage of oil frequently leads to disastrous consequences, resulting in massive economical losses and, more importantly environmental pollution. Developing oil sensors to diagnose an oil leak at an early stage before they cause widespread damage is crucial.[1] Petroleum hydrocarbons (HC) present a multiphase mix consisting of liquid, dissolved gaseous or solid phase in seawater [2] and direct oil sensors are used to detect methane, polyaromatic hydrocarbons, or hydrocarbons (HC) in seawater directly, while indirect oil sensors rely on discriminating the properties of the local seawater environment with and without the presence of oil.
The indirect methods may include measurement of seawater, physical properties (such as concentration of oxygen or CO2), optical light scattering, and under water microscopy. An optical light scattering method [3, 4] is also used to detect the scattered light or diffraction patterns of the suspended and undissolved materials in a water sample, while underwater microscopy [5-7] is used for analyzing microscopic organisms to support dispersant injections which reduce the oil to small droplets and increase microbial degeneration.[11, 12] The existing optical methods, which focus on detecting the particles or organisms in the water generally require highly sensitive/expensive sensors to identify the small sized particles and also suffer from time consuming and complicated data processing.
As defined in Wikipedia, graphene is an allotrope of carbon in the form of a two-dimensional, atom scale, hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes, including graphite, charcoal and carbon nanofibers and fullerenes. Graphene foam, taking advantages of its ultra-light weight,[13] high surface area and porous structure, has been recently proposed as a versatile and recyclable sorbent material. It shows highly efficient absorption of petroleum products (up to 86 times of its own weight), requiring no further pretreatment, which is tens of times higher than that of conventional absorbers.[14-17] Additionally, via simple heat treatment, the graphene foam can be reused up to 10 or more times without a drop in performance.[14, 15] Hence, the graphene foam can have widespread potential applications in environmental protection.
In this application, Applicants present a novel study on the optical transmission and scattering properties of graphene foam. Clear changes in these optical effects occur due to the absorption of various oil species. The presence of oil droplets in graphene foam leads to much stronger scattering effects, a change that can be easily detected remotely via optic fibers and imaging systems. Imaging of oil soaked graphene foam in multiple optical microscope detection modes demonstrates the presence of oil droplets (causing scattering) and also aid in their identification. Therefore, with the graphene foam, the efficiency of current underwater microscope and scattering based oil spill detection methods can be enhanced.
A patentability search on the invention disclosed several patents of interest. To be more specific, Geun (KR20160031760 A) discloses a gas sensor using a graphene foam to detect leakage of liquid natural gas (LNG) and liquid petroleum gas (LPG) gas. In this disclosure the graphene foam is formed by growing graphene by making the graphene absorbed to a porous nickel foam and then removing the nickel foam by etching.
Luukkala et al. (U.S. Pat. No. 4,882,499) discloses a liquid detector utilizing fiber optics, by which the presence of oils and various solvents can be detected. The detector is internally safe because the optical fiber is an insulator and may therefore be used to monitor liquids involving fire or explosive hazards. The detector may be used to detect leakage when storing oils and solvents, because it reacts most rapidly with these liquids. The detector makes use of capillarity of a sensing pick-up thereof, the optical reflection coefficient of the pick-up material changing as the pick-up material comes into contact with the liquid to be detected.
Afzali et al. (U.S. Pat. No. 8,395,774) discloses a method of using an optical sensor, the optical sensor comprising a sensing surface of graphene foam, the sensing surface located on a substrate, includes determining a first optical absorption spectrum for the graphene layer by a spectrophotometer; adding an analyte, the analyte selected to cause a shift in the first optical absorption spectrum, to the graphene layer; determining a second optical absorption spectrum for the modified graphene layer by a spectrophotometer; determining a shift between the first optical absorption spectrum and the second optical absorption spectrum; and determining a makeup of the analyte based on the determined shift.
Shioda (JP 01203944 A) discloses an oil detection sensor. An oil absorbing layer absorbs on oil, and measurement light emitted from an incidence fiber is passed through a lens in the connector on the side of an incidence surface and reflected totally by a reflecting surface, converged by the lens of the connector on the side of a projection surface, and guided to a projection fiber, so that it is confirmed that the detection surface is not covered with oil. If oil leaks by being mixed with water owing to an unexpected accident, etc., the oil absorbing layer absorbs the oil selectively without absorbing the water, so the detection surface contacts the absorbed oil. Then the detection surface of the sensor 1 enters a partial reflecting state because the oil which contacts and covers the sensor is larger in refractive index than air contacting it normally. Consequently, reflected light which is guided to the projection fiber decreases in intensity level and a photodetection part detects the oil leakage.
In conclusion, Applicants propose a simple and innovative way to detect oil environment by using graphene foam through optical imaging, as well as light scattering method. Compared with the existing methods, which detect oil emulsions or organism in the water and often involve complicated data processing, the graphene foam's performance as an oil collector can enhance the oil signal, making the detection easier, faster and economizer. Moreover, different oils in graphene foam give different colors in optical images, providing the possibility to identify the oil species. Interestingly, under microscope imaging, oil droplets can be observed in the graphene foam, which enhance the scattering effects, leading to the changes in spectral transmission. Despite the changes, the characteristic shapes of the transmission spectra remain the same, as well as the relative relationships between different oils. Finally diffraction of the oil in graphene foam was studied and results suggest that effect can be used to detect oil in conjunction with present optic fiber based oil sensors.